1. Field of the Invention
This invention relates to an improved aquarium filter and more particularly to an improved biological filter for an aquarium and to a filtration unit which comprises said improved biological filter together with a mechanical filter.
2. Description of the Prior Art
It is well known that the water in an aquarium needs filtration both to maintain clarity and purity. In addition to a filter capable of removing solids from the water a biological filter is desirable to maintain its purity, the latter comprising a particulate material such as gravel or sand on which living bacteria can grow. It is also known that to promote the life cycle of the bacteria it is desirable that the biological filter medium should be intermittently exposed to air.